This application claims the benefit of Korean Application No. 2002-31291, filed Jun. 4, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to the field of controlling the rotation of an object, such as a motor or a roller used in an inkjet printer or the like, and more particularly, to a method and an apparatus to control the rotation position of an object.
2. Description of the Related Art
In certain instances, an inkjet printer must adopt a line printing method, as opposed to a page printing method, to print images, because of limited print head width. In an inkjet printer, sheets of paper must be repeatedly advanced, line after line, to print images. The advancing of the paper is achieved by contact between a line feed roller (or a paper feed roller) and a pressure roller, and rotation of the line feed roller. Here, the distance by which a sheet of paper is advanced is determined by the rotation amount of the line feed roller. If a sheet of paper is advanced slightly less than a predetermined amount, a black line is created between images. If the sheet of paper is advanced slightly more than the predetermined amount, a white line is created between images. Therefore, the degree of precision with which the rotation of the line feed roller is controlled directly affects the quality of the images printed by the inkjet printer.
In general, methods of controlling the amount of rotation of an object to be controlled, for example, a motor used in an inkjet printer, can be roughly classified as either direct or indirect methods. In a direct method, an offset error occurs due to nonlinear components, such as variations in friction load or changes in the characteristics of a motor in a normal state. In an indirect method, a speed profile is made until a motor reaches a normal state and the motor follows the speed profile to thus indirectly reach a desired rotation position. In other words, in an indirect method, a speed profile is first drawn up, and then a motor follows the speed profile in order to go from rotation position A to rotation position B. For example, in a conventional indirect method of controlling the rotation of a motor, an error speed e(kT) between a real speed v(kT) and a desired speed V(kT) of the motor is obtained, and then a voltage u(kT) to be applied to the motor is generated using an cumulative error speed value xcexa3e(kT) and an error speed e(kT), as given by Equation 1:
u(kT)=KPe(kT)+KIxcexa3e(kT)xe2x80x83xe2x80x83(1) 
wherein KP and KI are weights. In this conventional method of controlling the rotation position of a motor, Equation 1 is repeatedly calculated at intervals of a predetermined length of time until the motor goes from rotation position A to rotation position B.
FIG. 1 is a graph for explaining a conventional indirect method of controlling the rotation position of an object, in which the rotational speed of the object to be controlled is plotted on the vertical axis and time is plotted on the horizontal axis. As shown in FIG. 1, the rotation speed of the object begins to be reduced at time kxc2x7Ts, not at time t1 between (kxe2x88x921)xc2x7Ts (k is an integer) and kxc2x7Ts, although speed reduction is required to commence at t1 in order to stop the rotation of the object at the proper position. This is because in the conventional method of controlling the rotation position of the object, Equation 1 is calculated at intervals of Ts to generate a voltage necessary to control the object. As a result, the object does not stop rotating until it has rotated a distance equal to the area of hatched region 2 in FIG. 1, beyond a desired stopping position. To prevent this error, the predetermined period of time (Ts) can be reduced in consideration of several conditions, such as the performance of a central processing unit (CPU, not shown) and the time required for calculating Equation 1. However, if the predetermined period of time (Ts) is reduced, the CPU, which also performs other operations, has an increased burden.
Also, although the speed of the object must be reduced within a short time after kxc2x7Ts, the conventional indirect method of controlling the rotation position of an object takes significant time to calculate the cumulative error speed value xcexa3e(kT) to obtain the voltage (as shown in Equation 1) to control the rotation of the object. Thus, since speed reduction cannot commence immediately, final stoppage of rotation is delayed.
Moreover, the length required for stopping the object increases due to the delay of speed reduction, and thus an error in position at which the object should stop increases.
Accordingly, it is an object of the present invention to provide a method of controlling the rotation position of an object that enables the rotated object to be accurately and precisely stopped at a desired position.
It is another object of the present invention to provide an apparatus to control the rotation of an object that enables the rotated object to be accurately and precisely stopped at a desired position.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
The foregoing and/or other objects of the present invention are achieved by providing a method of controlling a rotation position of an object, the method including measuring first and second actual control variables which vary as the object rotates; determining whether the first actual control variable is smaller than a predetermined amount; determining whether a period of time has elapsed if it is determined that the first actual control variable is smaller than the predetermined amount; and obtaining a difference between a physical quantity that is generated corresponding to the first actual control variable and the second actual control variable, and determining a control amount to control the object using the obtained difference, if it is determined that the period of time has elapsed or the first actual control variable is larger than the predetermined amount, wherein the predetermined amount corresponds to a position at which the object is rotated to stop the object at a desired position.
The foregoing and/or other objects of the present invention are also achieved by providing an apparatus to control a rotation position of an object, the apparatus including a control variable measuring unit which measures first and second actual control variables that vary as the object rotates; a control signal generator which compares the first actual control variable input from the control variable measuring unit with a predetermined value and outputs the result of the comparison as a control signal; and a control amount determiner which compares the second actual control variable with a physical quantity that is generated corresponding to the first actual control variable at regular intervals of a period of time or irregularly in response to the output control signal, and determines a control amount from a result of the comparison, wherein the object operates in response to the control amount.